This invention relates to a fire-resistant thermoplastic composition and more particularly to a composition useful to form interlayers for use in safety glass laminates.
Shatter-resistant, optically clear, laminated safety or security glass containing one or more thermoplastic interlayers between and adhered to opposing panes of glass (or to one glass panel and to another opposing rigid thermoplastic member) is well known for use principally as windows in vehicles and commercial and private buildings. When such safety glass is exposed to fire in an emergency, the glass cracks almost immediately and the interlayers usually used melt, start to drip through the cracks and flow to the base of the assembly followed often by complete burning, usually in a few minutes, depending on exposure time and flame temperature. Continued exposure results in pieces of the glass falling away and eventual disintegration of the laminate. In the absence of any window protection at all, smoke is then free to flow unchecked throughout the interior of the structure where the assemblies were mounted which increases the safety hazard to occupants who might be trapped therein. Furthermore, the absence of any barrier to the outside atmosphere permits oxygen to feed the fire to aggravate the conflagration.
Attempts to overcome this have involved the use of wired glass where a wire mesh is employed to provide strength to the window panel during fire exposure but the visually apparent wire mesh tends to detract from the aesthetics of the window. Interlayers, believed to be inorganic, and gels are offered commercially as substitutes for conventional interlayers in safety glass windows which are designed to foam in place between the glass panes when the assembly is exposed to fire to provide fire resistance to the laminate. These special interlayers and gels are very costly and in normal, non-fire use have more color (yellowness) and reduced weatherability (i.e resistance to UV light) than do conventional safety glass interlayers.